Though the days of a guaranteed, year-long-plus recovery from a torn ACL continue to fade into the past, recoveries that exceed 12 months are still not uncommon. Additional ligament injury can also complicate matters.
In other words, when Gronkowski went down last week with both a torn ACL and MCL, the start of his 2014 season fell into very real doubt. A look at the injuries themselves explains why.
Isolated Anterior Cruciate Ligament (ACL) Injuries
The other near-absolute certainty?
Ruptured ACLs do not heal on their own. Rather, doctors must wholly reconstruct the ligament. To do so, they use the athlete's own tissue.
On the operating table, surgeons like Dr. James Andrews frequently take a piece of the patellar tendon—the part of the knee a doctor hits with a reflex hammer—to, quite literally, replace the native ACL.
Over the next months and years, the body transforms the tendon into tissue more closely resembling the original ligament through a process called "ligamentization."
Following surgery, athletes move on to rehab. Range of motion, strength training and agility exercises dominate the better part of the next year.
A quick glance through recent ACL recovery times in the NFL reveals a very rough average of 10 months to go from the operating table to the line of scrimmage.
Isolated Medial Collateral Ligament (MCL) Injuries
Isolated MCL injuries come in three different grades: 1, 2 and 3.
Grade 1 sprains represent minor ligament overstretches without obvious tearing.
On the other hand, a Grade 2 sprain implies a partial ligament tear. If a complete rupture occurs, the diagnosis moves to Grade 3.
Most of the time, MCL injuries do not require surgery—even in the case of a full tear.
Instead, NFL athletes usually only need one or two weeks to rehab a Grade 1 sprain. The timeline extends to around a month following a partial tear, and a complete injury can take upward of two to three.
Rob Gronkowski's Case: ACL/MCL Combo
Unfortunately, simultaneous injury to the ACL and MCL is not an uncommon event. Human anatomy makes it so forceful hits to the outside of the knee can stretch—and cause injury to—both ligaments at the same time.
Concurrent ACL and MCL injuries occur frequently enough that the combination—along with a meniscus injury—has earned the nickname of "the unhappy triad" throughout the medical community.
Fortunately, an ACL/MCL combo does not necessarily carry a longer recovery time when compared to an ACL alone.
Then again, sometimes it does.
Dr. Bert Mandelbaum—a renowned orthopedic surgeon out of the Institute for Sports Sciences in Los Angeles—weighed in on the issue. As expected, the extent of damage is important.
"It matters what the severity is [...]," he explained. "If there is a complete medial column avulsion—including the deep and superficial MCL and posterior oblique ligament—we repair all the medial column structures immediately and do the ACL reconstruction four to six weeks later when good range of motion is achieved."
In other words, if the MCL injury involves additional surrounding structures—rather than just the MCL itself—the repair of an ACL may need to wait for more than a month.
Mandelbaum added that he and other experts within the orthopedic surgery field now know that in such a situation, a delayed ACL repair provides an athlete with the best opportunity to regain normal range of motion and functional performance.
Sometimes, surgeons may even decide to wait for an athlete to complete a few weeks of therapy before operating—even if an injury involved only the ACL.
According to Mandelbaum, operating immediately or first working on rehab carry similar clinical outcomes.
What does this mean for Gronkowski?
Simple. The road ahead is not easy.
Using an approximate 10-month rehab time, an immediate ACL repair—similar to when Dr. Andrews operated just a few days after Adrian Peterson tore his ACL and MCL in Dec. 2011—would have Gronkowski back on the field by Sept. 2014.
Conversely, a complicated MCL injury—involving surrounding bone or other ligaments—could delay the Patriots tight end's ACL reconstruction by several weeks. In this scenario, an average recovery time keeps him off the field until mid- to late October.
As always, exact medical details are not available to the public, and only the Patriots medical staff knows Gronkowski's true diagnosis.
Furthermore, individual surgeons usually adhere to their own preferences and protocols—admittedly evidence-based, but still preference-dependent.
Nevertheless, even in the best-case scenario, everything will need to go exactly right for Gronkowski to be ready by Week 1. The opposite scenario could leave him sidelined for most or all of 2014.
More than likely, he will land somewhere in the middle.
The worst part? No one—not the Patriots, not Patriots fans and not even necessarily his medical staff—will know for certain for some time still.
Said another way?
Let the waiting game begin.
Dr. Dave Siebert is a resident physician at the University of Washington. He plans to pursue fellowship training in Primary Care (non-operative) Sports Medicine.
All quotes were obtained firsthand.